Search results for "METASTABILITY"
showing 10 items of 262 documents
Electron Binding in a Superatom with a Repulsive Coulomb Barrier: The Case of [Ag44(SC6H3F2)30]4– in the Gas Phase
2020
The electron binding mechanism in [Ag44(SC6H3F2)30]4- (SC6H3F2 = 3,4-difluorobenzenethiolate) tetra-anion was studied by photoelectron spectroscopy (PES), collision-induced dissociation mass spectrometry (CID-MS), and density functional theory (DFT) computations. PES showed that [Ag44(SC6H3F2)30]4- is energetically metastable with respect to electron autodetachment {[Ag44(SC6H3F2)30]3- + e-} and features a repulsive Coulomb barrier (RCB) with a height of 2.7 eV. However, CID-MS revealed that [Ag44(SC6H3F2)30]4- does not release an electron upon collisional excitation but undergoes dissociation. DFT computations performed on the known structure of [Ag44(SC6H3F2)30]4- confirmed the negative a…
Axialisation, cooling and quenching of $\mathsf{Ba^+}$ ions in a Penning trap
1998
Collisions of ions, stored in a Penning trap, with neutral background molecules usually lead to rapid ion loss from the trap unless the ions are excited by the sum of the frequencies of the reduced cyclotron and magnetron motion. Then the ions are cooled by collisions and are driven to the trap centre leading to substantial increase of the storage time. Furthermore in a three level system including a long living metastable state collisions deexcite this metastable state and increase the population density in the ionic ground state. In a laser spectroscopic experiment we demonstrate the advantages of collisions on Ba+ ions stored in a Penning trap. The combined action of metastable state que…
Seed- and wall-induced heterogeneous nucleation in charged colloidal model systems under microgravity
2011
Understanding the process that drives an undercooled fluid to the crystal state is still a challenging issue for condensed matter physics and plays a key role in designing new materials. The crystallization kinetics and the resulting polycrystalline morphology are given by a complex interplay of crystal nucleation, growth, and ripening. A great deal of progress has been made in recent years using colloidal suspensions as model systems in the study of crystallization. Close analogies to atomic systems are observed which can be exploited to address questions not accessible in atomic solidification. Here we present systematic measurements of the crystallization kinetics of a charged colloidal …
Mass spectra of chlorinated esters: 2—Methyl mono- and dichlorobutanoates
1982
The mass spectral fragmentations of methyl mono- and dichlorobutanates have been studied. Deutrium labelling and metastable ion analysis were used to elucidate the fragmentation mechanisms. The molecular ion peaks of the esters are weak and show only in the spectra of the monochloro isomers. A McLafferty rearrangement gives the base peaks in the spectra of methyl 2-chloro-, 4-chloro- and 4,4-dichlorobutanoate; α-cleavage, [COOCH3]+, in methyl 2,2- and 2,4-dichlorobutanoate; [MCl]+, in methyl 3-chlorobutanoate; [MClHCl]+, in methyl 3,4-dichlorobutanoate; [MClCH2CO]+, in methyl 3,3-dichlorobutanoate and [MClCOOCH3]+˙, in methyl erythro- and threo-2,3-dichlorobutanoate. The mass spectra of the…
Metastability and Relaxation in Quantum and Mesoscopic Systems
2013
The transient dynamics and the relaxation of three quantum and mesoscopic systems are investigated. In particular we analyze: (i) a long Josephson junction (LJJ) driven by a non-Gaussian Lévy noise current; (ii) a metastable quantum dissipative system driven by an external periodical driving; and (iii) the electron spin relaxation process in n-type GaAs crystals driven by a fluctuating electric field. Specifically, in the first system the LJJ phase evolution is described by the perturbed sine-Gordon equation. We find the noise enhanced stability and resonant activation phenomena, by investigating the mean escape time as a function of the bias current frequency, noise intensity and length of…
Domain Wall Spin Structures in Mesoscopic Fe Rings probed by High Resolution SEMPA
2016
We present a combined theoretical and experimental study of the energetic stability and accessibility of different domain wall spin configurations in mesoscopic magnetic iron rings. The evolution is investigated as a function of the width and thickness in a regime of relevance to devices, while Fe is chosen as a material due to its simple growth in combination with attractive magnetic properties including high saturation magnetization and low intrinsic anisotropy. Micromagnetic simulations are performed to predict the lowest energy states of the domain walls, which can be either the transverse or vortex wall spin structure, in good agreement with analytical models, with further simulations …
Resistive state relaxation time in ZrO2(Y)-based memristive devices under the influence of external noise
2022
The effects of external digitally synthesized Gaussian noise on the resistive state relaxation time of a ZrO2(Y)-based memristive device when switching from a low resistance state to a high resistance state have been experimentally investigated. A nonmonotonic dependence of the resistive state relaxation time on the external noise intensity is found. This behavior is interpreted as a manifestation of the noise-enhanced stability effect previously observed in various complex systems with metastable states. It is shown that the experimental results agree satisfactorily with the theoretical ones. The presented results indicate the constructive role of external noise and its possible use as a m…
Field theoretic study of bilayer membrane fusion: I. Hemifusion mechanism
2003
Self-consistent field theory is used to determine structural and energetic properties of metastable intermediates and unstable transition states involved in the standard stalk mechanism of bilayer membrane fusion. A microscopic model of flexible amphiphilic chains dissolved in hydrophilic solvent is employed to describe these self-assembled structures. We find that the barrier to formation of the initial stalk is much smaller than previously estimated by phenomenological theories. Therefore its creation it is not the rate limiting process. The barrier which is relevant is associated with the rather limited radial expansion of the stalk into a hemifusion diaphragm. It is strongly affected by…
Single Particle Jumps in a Binary Lennard-Jones Glass
2002
ABSTRACTWe study a binary Lennard-Jones mixture below the glass transition with molecular dynamics (MD) simulations. To investigate the dynamics of the system we define single particle jumps via their single particle trajectories. We find two kinds of jumps: metastable jumps, where a particle jumps back and forth between two or more states, and real jumps, where a particle does not return to any of its former states. For both the real and metastable jumps we present as a function of temperature the number of jumps, jump size, time between jumps, and energy.
Memristors and nonequilibrium stochastic multistable systems
2022
The main aim of this special issue is to report the recent advances and new trends in memristors and nonequilibrium stochastic multistable systems, both theoretically and experimentally, within an interdisci-plinary context. In particular, memristors are multistable systems whose switching dynamics is a stochastic process, which can be controlled by internal and external noise sources, unveiling the constructive role of random fluctuations. Furthermore, the use of memristors as memory elements in neuromorphic systems with noise-assisted persistence of memory states, chaotic dynamics, metastable chaos and chaos synchronization, new stochastic nonlinear models, noise-induced phenomena such as…